A plasma display panel (hereinafter referred to as a “PDP”) displays images including characters or graphics by light-emitting phosphors with ultraviolet of 147 nm generated during the discharge of a mixed inert gas such as He+Xe, Ne+Xe or He+Ne+Xe. This PDP can be easily made thin and large, and it can provide greatly increased image quality with the recent development of the relevant technology. More particularly, a three-electrode AC surface discharge type PDP has advantages of lower voltage driving and longer product lifespan since wall charges are accumulated on a surface upon discharge and electrodes are protected from sputtering generated by a discharge.
FIG. 1 is a perspective view illustrating the structure of a discharge cell of a three-electrode AC surface discharge type PDP in the related art.
Referring to FIG. 1, the discharge cell of the three-electrode AC surface discharge type PDP comprises scan electrodes Y and sustain electrodes Z formed on a bottom surface of an upper substrate 10, and address electrodes X formed on a lower substrate 18. The scan electrode Y comprises a transparent electrode 12Y, and a metal bus electrode 13Y, which has a line width smaller than that of the transparent electrode 12Y and is disposed at one side edge of the transparent electrode. Furthermore, the sustain electrode Z comprises a transparent electrode 12Z, and a metal bus electrode 13Z, which has a line width smaller than that of the transparent electrode 12Z and is disposed at one side edge of the transparent electrode.
The transparent electrodes 12Y, 12Z are generally formed of Indium Tin Oxide (ITO) and are formed on a bottom surface of the upper substrate 10. The metal bus electrodes 13Y, 13Z are generally formed of metal such as chromium (Cr) and are formed on the transparent electrodes 12Y, 12Z. The metal bus electrodes 13Y, 13Z serve to reduce a voltage drop caused by the transparent electrodes 12Y, 12Z having high resistance. On the bottom surface of the upper substrate 10 in which the scan electrodes Y and the sustain electrodes Z are formed parallel to each other is laminated an upper dielectric layer 14 and a protection layer 16. Wall charges generated during the discharge of plasma are accumulated on the upper dielectric layer 14. The protection layer 16 functions to prevent the upper dielectric layer 14 from being damaged by sputtering generated during the discharge of plasma and also to improve emission efficiency of secondary electrons. Magnesium oxide (MgO) is generally used as the protection layer 16.
A lower dielectric layer 22 and barrier ribs 24 are formed on the lower substrate 18 in which the address electrodes X are formed. A phosphor layer 26 is coated on the surfaces of the lower dielectric layer 22 and the barrier ribs 24. The address electrodes X are formed to cross the scan electrodes Y and the sustain electrodes Z. The barrier ribs 24 are formed parallel to the address electrodes X and function to prevent ultraviolet generated by a discharge and a visible ray from leaking to neighboring discharge cells. The phosphor layer 26 is excited with an ultraviolet generated during the discharge of plasma to generate any one visible ray of red, green and blue. An inert mixed gas is injected into discharge spaces provided between the upper substrate 10 and the barrier ribs 24 and between the lower substrate 18 and the barrier ribs 24.
The PDP is time driven with one frame being divided into several subfields having a different number of emissions in order to implement gray levels of an image. Each of the sub fields is divided into a reset period for initializing the entire screen, an address period for selecting a scan line and selecting a cell from the selected scan line, and a sustain period for implementing gray levels according to a discharge number.
The reset period is divided into a set-up period where a ramp-up waveform is applied, and a set-down period where a ramp-down waveform is applied. For example, if it is sought to display an image with 256 gray levels, a frame period (16.67 ms) corresponding to 1/60 seconds is divided into eight subfields (SF1 to SF8), as shown in FIG. 2. Each of the subfields (SF1 to SF8) is divided into a reset period, an address period and a sustain period as described above. The reset period and the address period of each of the subfields (SF1 to SF8) are the same every subfield, whereas the sustain period is increased in the ratio of 2n (where, n=0, 1, 2, 3, 4, 5, 6, 7) in each subfield.
FIG. 3 shows a waveform for illustrating a method of driving a PDP in the related art.
Referring to FIG. 3, the PDP is driven with one frame being divided into a reset period for initializing the entire screen, an address period for selecting a cell, and a sustain period for sustaining the discharge of a selected cell.
In a set-up period of the reset period, a ramp-up waveform (Ramp-up) is applied to the entire scan electrodes Y at the same time. The ramp-up waveform (Ramp-up) causes a weak discharge to be generated in the cells of the entire screen, so that wall charges are generated in the cells. In a set-down period, after the ramp-up waveform (Ramp-up) is applied, a ramp-down waveform (Ramp-down), which falls from a positive (+) voltage lower than a peak voltage of the ramp-up waveform (Ramp-up), is applied to the scan electrodes Y at the same time. The ramp-down waveform (Ramp-down) generates a weak erase discharge within the cells, thus erasing unnecessary charges, such as wall charges generated by the set-up discharge and spatial discharges, and causing wall charges necessary for an address discharge to uniformly remain within the cells.
In the address period, while a negative (−) scan pulse is sequentially applied to the scan electrodes Y, a positive (+) data pulse (Data) is applied to the address electrodes X. As a voltage difference between the scan pulse (Scan) and the data pulse (Data) and a wall voltage generated in the reset period are added, an address discharge is generated within the cells to which the data pulse (Data) is applied. Wall charges are generated within cells selected by the address discharge.
Meanwhile, during the set-down period and the address period, a positive (+) sustain voltage (Vs) is applied to the sustain electrodes Z.
In the sustain period, a sustain pulse (Sus) is alternately applied to the scan electrodes Y and the sustain electrodes Z. A sustain discharge is generated in surface discharge form between the scan electrodes Y and the sustain electrodes Z in cells selected by the address discharge whenever the sustain pulse (Sus) is applied as the wall voltage within the cell and the sustain pulse (Sus) are added. Lastly, after the sustain discharge is finished, an erase ramp waveform (erases) having a narrow pulse width is applied to the sustain electrodes Z, thus erasing wall charges within the cells.
In the method of driving the PDP in the related art, however, loss of power is consumed because the ramp-up waveform (Ramp-up) having a high voltage value must be applied to the scan electrodes Y every subfield. Furthermore, a large amount of light is generated by the ramp-up waveform (Ramp-up) applied to the scan electrodes Y during the reset period, which results in lowered contract. Therefore, a problem arises because a high contrast image cannot be displayed.